Effect of the Porcine IGF2 Intron3-G3072A Substitution on Carcass Cutability and Meat Quality

Abstract Text: A single-nucleotide polymorphism (SNP) in a regulatory region of intron 3 within the IGF2 gene (IGF2 G3072A) accounts for 4-5% of the variability in loin eye area and 7-21% of the variability in back fat thickness in pigs.  However, data are limited regarding carcass composition and fresh meat quality characteristics of pigs with differing paternally expressed alleles for this IGF2 variant. A single heterozygote (AG) Berkshire boar was bred to homozygous (AA) commercial Yorkshire-cross sows producing an F₁ generation from which approximately 50% of possessed a paternal G allele and 50% possessed a paternal A allele. These offspring, barrows and gilts, were group housed, fed ad libitum a diet that met or exceeded NRC nutrient recommendations, and were slaughtered at 176 days (+/- 4) of age. Pig was treated as the experimental unit. Lean cutting yield determination was completed on the right side of chilled carcasses approximately 24 hours after slaughter.  Fresh loin  quality was assessed on the left side of the carcass at the level of the 10^th rib.  Quality analyses included 24-hour pH, drip loss, objective color (Minolta L^*, a^*, and b^*), subjective color, marbling and firmness, cooking loss, and shear force at 1, 3, 7, 14 and 21 days after slaughter. Ending live weight and hot carcass weights were not affected by IGF2 allele; however, tenth rib back fat thickness decreased by approximately 0.4 cm (P < 0.05), loin eye area increased by approximately 4.0 cm² (P < 0.05), and predicted fat free lean increased over 2 percentage units (P < 0.05) in pigs that possessed paternal A alleles compared to G alleles.  Furthermore, boneless lean cuts from the shoulder, loin and ham were heavier (P < 0.05) in pigs with paternal A alleles compared to G alleles. In general, IGF2 allele had minimal effects on fresh loin quality as 24-hour pH, drip loss, and objective color were not different (P > 0.05) in the IGF2 variants. Minolta L* value was increased by approximately 2.5 L* units (P < 0.05), and cooking loss was increased by approximately 1.5 percentage units (P < 0.05) in pigs carrying the paternal A allele compared to the G allele.  Together these data suggest that the IGF2 G3072A mutation is responsible for a significant increase in lean meat yield with little impact on fresh meat quality.

Keywords: Insulin Growth Factor 2, IGF2 G3072A, SNP, Cutting Yield